A common analytical procedure is the trapping and analysis of reaction products. Testing and evaluating the toxicity of combustion products emitted by fires, for example, has led to the development of various devices for simulating combustion conditions and collecting the products. The accuracy of subsequent qualitative and quantitative analyses of the combustion products depends on whether the products have been modified before collection and on whether substantially all the products have been trapped and collected.
Combustion product analysis is not limited to determining the amount of carbon dioxide, carbon monoxide, oxygen and water generated, but includes the identification and quantification of biologically hazardous materials contained in the products for toxicity studies. For example, the characterization of the products emitted from burning polymers is necessary for limiting the use of polymers in certain applications.
In addition to combustion product analysis a need exists for the testing of products generated by other chemical reactions, especially high temperature decomposition processes. For example, pyrolysis and certain metallurgical processes such as sintering may emit toxic products requiring identification.
Thus, a device for the efficient and accurate collection of various chemical reaction products and especially for the creation and trapping of products formed by combustion and high temperature decomposition processes is necessary for meaningful subsequent analysis.
The generation and collection of thermal combustion products for analysis has commonly been accomplished using devices which incorporate the method described in DIN 53436. Such devices consist of a long, horizontal quartz combustion tube in which a sample placed in an airstream is continuously decomposed by means of an external moving furnace. The effluents are carried by the airstream from the tube to an external analytical measuring system or, alternatively, are measured by on-line monitors such as infrared detectors.
Problems associated with using the DIN 53436 apparatus include inaccurate qualitative and quantitative analyses of the decomposition products due to the great amount of soot and smoke emitted during combustion of the sample. Such materials strongly adhere to surfaces even slightly cooler than the region in which they were generated. Thus, not all the decomposition products will exit the tube for analysis, and results will be inaccurate. Conventional solvent washing of the combustion tube to collect the adhered material will not increase accuracy because much of the product may polymerize upon contact with the cooler walls of the decomposition tube and remain adhered to the surface.
Another source of error in the analysis of the decomposition products comes from the long transportation time (typically between 25 and 35 minutes) between sample decomposition and product collection. Since the products remain heated at high temperatures while they are slowly carried along the length of the tube, the initial products may polymerize or otherwise be altered before analysis. Thus, the results obtained may include identification of species not actually produced during sample decomposition.
Finally, cleaning the apparatus following the decomposition process is both time-consuming and cumbersome. Since solvent washing will not remove the surface contamination, the components of the device must be reheated in oxygen to temperatures approximating 500.degree. C. to burn off the polymer. Thus, evaluation of multiple samples on the same apparatus in a short amount of time is impossible.
The present invention is a device designed in part to overcome the problems encountered when using conventional apparatus, such as that employed according to DIN 53436 for trapping thermal decomposition products. Sampling of both the organic and inorganic components is more accurate because all the product is collected without modification. The total time from decomposition of the sample to collection is typically less than 10 min; therefore, the products are not likely to polymerize before collection. Also, the apparatus maintenance and cleaning time is greatly reduced.
Reaction gases are channeled from top to bottom of an externally heated vertical external tube by slightly pressurizing the products. Thus, the products do not adhere to the inner walls of the external tube but are forced into a region of decreased diameter at the lower end of the tube. Two concentric tubes reside within the narrow portion of the external tube to trap the products. Introduction of a shield gas at the lower end of the external tube prevents product adherence to both the decreased diameter portion of the external tube and the concentric tubes. The concentric tubes are flushed with water and cooled such that soluble decomposition products are trapped in the water and collected for analysis. Insoluble products remain suspended in the water and may be separated externally. The gaseous products are collected by vacuum after passing through the stream of water.
The use of water in the present invention to trap the reaction products is advantageous in that system temperatures much greater than 1000.degree. C. may be reached in heating the sample. By using an external tube and a sample introduction apparatus consisting of a ceramic material which is heat resistant at high temperatures, the system is made adaptable to such decomposition processes as combustion, sintering or pyrolysis. Because the water cools the concentric tubes through which the products pass before leaving the system, the concentric tubes and the collection vessel may consist of a material such as quartz or glass that is not physically resistant to very high temperatures.
Trapping the reaction products with water is also advantageous because, for example, the actual physiological situation where combustion products are breathed into the lungs is more accurately simulated in the present invention that in the DIN 53436 device. Finally, in the case of combustion where water is a major product of the process, its introduction to trap the sample product adds no new components to the product composition.